Studies Suggest Better Approaches to Staying Clot-Free

One trial found gene tests help with standby med warfarin, another shows promise for newer drug

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Doctors used two specific genes associated with the blood-clotting process to help determine the amount of medication a person would receive, Pirmohamed said.

Patients with a genetically guided warfarin dose remained within the therapeutic sweet spot for 67 percent of their three-month-long treatment, compared with 60 percent for people taking warfarin without the genetic guidance.

Patients with genetic dosing reached that sweet spot about 28 percent more quickly, Pirmohamed said. They also were able to begin a stable long-term dose about 25 percent more quickly. In addition, they required 9 percent fewer dose adjustments.

The researchers used a limited genetic test that costs about $67.

A U.S. expert said genetic testing is likely to become much more useful in determining drug dosage in the future, given that the costs of such tests are falling.

A test that can reveal a person's entire genetic code currently costs about $1,000 -- down from $80,000 a few years ago, said Dr. Joseph Loscalzo, chairman of the department of medicine and physician-in-chief at Brigham and Women's Hospital in Boston. Loscalzo, who also is editor-in-chief of the journal Circulation, said he expects that one day such a test could cost as little as $100.

MedStar's Howard said a person would only need one genetic test to help guide their therapy. After all, genetics do not change.

The picture regarding these tests remains hazy, however. A related study, led by Dr. Stephen Kimmel, of the University of Pennsylvania Perelman School of Medicine, was presented Tuesday at the AHA meeting. The study of nearly 1,000 patients found no significant difference between those whose warfarin dose was based on genetic testing and those with doses set using current guidelines.

In that study, both groups of patients were in the therapeutic sweet spot about 45 percent of the time.

The difference between the two studies might be the other factors beyond genetics that can determine warfarin dosing, said Dr. Patrick Ellinor, a cardiologist at the Massachusetts General Hospital Heart Center.

Those factors can include the age, weight and race of the patient, as well as whether they smoke or have other health risks. "That's just as helpful as the genetic information, and we should be using it," said Ellinor, who also is an associate professor at Harvard Medical School.